Alaalatoa missed their final-round loss to the Crusaders with a calf strain, but Larkham says his leadership is vital as the Brumbies look to see off the Hurricanes on Saturday night in Canberra.
"He's had a good week so ticked everything off in terms of all the rehab markers with his strength, running, contact so he's ready to go," Larkham said of the Wallabies prop.
"He's always been an outstanding rugby player but the leadership qualities that he brings to the team, the confidence that he gives the other players is certainly something that we're going to benefit from this weekend."
In a quirk of the new six-team finals system and the scheduling of the finals, the third-placed Brumbies will know before kick-off whether they have a place in the semi-finals.
There are three qualifying finals and all winners plus the top-ranked loser will advance.
But Larkham said the Brumbies wanted to field their best team available and target a win regardless of the outcome of the other matches.
"We are the last game this weekend but we've been pretty firm on making sure that we get a good performance out there on the field so irrespective of the other results we need to know that we're playing well," the coach said on Wednesday.
"We can't get distracted by these other games and the other results.
"The most important thing for us right now is to focus on our preparation so that we can have our best performance this weekend and either way we're going out there to try and win the game."
In the only change to the starting side, Feao Fotuaika, who scored in the 33-31 loss to the Crusaders, will make way for Alaalatoa and return to the bench, bumping Rhys Van Nek out of the squad.
Larkham said his team wanted a better first half after they trailed the Crusaders 14-25 at halftime while they were also down at the break in their last clash with the Hurricanes, which they also lost.
He said with the Kiwi teams playing a similar fast and physical style, the Brumbies would be ready.
"They're a physical side, the contests at the breakdown are very similar to Crusaders," Larkham said.
"They're very good with the ball in hand, they've got dangerous threats around the ruck ... and they've got the ability to shift the ball quite well.
"We've come across teams that play this way a few times this year and hopefully that's put us in a good position to play well this weekend."
Brumbies: James Slipper, Billy Pollard, Allan Alaalatoa, Nick Frost, Tom Hooper, Rob Valetini, Rory Scott, Tuaina Taii Tualima, Ryan Lonergan, Noah Lolesio, Corey Toole, David Feliuai, Len Ikitau, Andy Muirhead, Tom Wright. Reserves: Lachlan Lonergan, Lington Ieli, Feao Fotuaika, Lachlan Shaw, Luke Reimer, Harrison Goddard, Declan Meredith, Ollie Sapsford.
Hurricanes: Xavier Numia, Asafo Aumua, Tyrel Lomax, Zach Gallagher, Caleb Delany, Devan Flanders, Du'Plessis Kirifi, Peter Lakai, Cam Roigard, Brett Cameron, Fatafehi Fineanganofo, Peter Umaga-Jensen, Billy Proctor, Bailyn Sullivan, Ruben Love. Reserves: Raymond Tuputupu, Tevita Mafileo, Pasilio Tosi, Hugo Plummer, Brad Shields, Ereatara Enari, Ngatungane Punivai, Callum Harkin.
